I purchased a genuine Bosch unit w/ a warranty off Partsgeek.com
Scroll to the bottom for the Bosch. There is also a Valeo (which I would consider) for a couple bucks less.
http://www.partsgeek.com/catalog/200...lternator.html


Or you can try here: Be prepared to pay more $$
http://www.roverparts.com/nxt/?keywo...very+Series+II

 

You can find them used, but personally I'd buy a reman or new. Coors posted a good link there, that's the best price I've seen, but you could also call the local auto parts stores and see what their prices on a reman unit would be.

 

Before you spend $ on replacing the alt. Get a mechanic's stethoscope from Harbor Freight or grab a screwdriver and put it to the alt and put your ear to the end. You will hear the squeak if its the alt.